The present invention relates to a combined mechanical, hydraulic and pneumatic control system to control the delivery of air pulses to the jet air twist devices in a yarn production system.
In the use of yarn, particularly artifical fibers, it is sometimes desirable that the yarn have bulk which may add to its appearance, wearability and texture. It has been suggested that a desirable method of yarn processing is to give each individual strand of yarn a "false-twist", in which a strand is twisted at a point generating opposite twists above and below the point of twisting the yarn, which is its "node". Each of the "false-twist" yarns has both an "S" twist and a "Z" twist, the "S" and "Z" referring to the direction of the helices of the twisted strands.
It has also been suggested that there be a joinder and locking of two of the false-twisted yarns at their nodes, for example, by plying the two yarns together to form a "self-twist" yarn.
In the applicants' copending prior application Serial No. 755,671, entitled "Self-Twist Plural Yarn Strand System", filed Dec. 30, 1976, the subject matter of which is incorporated by reference herein, slivers of yarns from separate sliver containers are pulled between drafting rolls to draw the yarn, and the drawn yarn strands are each brought to a primary twist jet. The yarn is then brought to false-twist jets which form a false-twist yarn, and then to a wire guide. The wire guide positions the two strands over a yarn wheel which carries an abrasive rotating disc, the direction of rotation being about a radius of the yarn wheel. The abrasive disc plies together the two yarns at the nodes. The joined yarn may then be pulled through a heat-setting apparatus and wound on a bobbin. That application, at its FIGS. 7 through 11, as filed, describes one embodiment of a vortex jet device which produces a false twist of a single yarn before locking and self-twisting. The jet device has two inlets to permit control of twist in both the "S" and "Z" directions.
Other designs of pneumatic vortex jet devices for producing a false twist or a twist between two yarns or the joining of two or more yarns have also been shown in various prior patents; for example, such fluid jet false twisting devices are shown in U.S. Pat. No. 2,515,299 to B. H. Foster et al.; U.S. Pat. No. 3,079,745 to A. L. Breen et al.; U.S. Pat. No. 3,116,588 to A. L. Breen et al.; U.S. Pat. No. 3,206,922 to K. Nagahaha et al.; U.S. Pat. No. 3,940,917 to D. R. Strachan; and U.S. Pat. No. 3,353,344 to F. J. Clendening, Jr. In FIG. 5 of the Clendening patent there is shown a multiplicity of such jet twisters, all of which operate from a common source of air. In U.S. Pat. No. 3,775,955 to J. J. Shah, a jet block receives air from a common source. The air is delivered through four air lines, each of which is separately controlled by an electric solenoid switch, the switches being controlled in turn by a set of cams.
A difficulty with the type of control apparatus shown in the Shah '955 patent would be that the length of tubings between the compressed air source and the plurality of twisting jet devices is unequal; that is, some of the compressed air lines are longer than other of the compressed air lines. Since air is a compressible fluid, there may occur a large difference in transport time between the control devices, which, in the case of Shah, are the solenoids, and the outlets of the air lines. This difference of timing may result in a non-uniformity of yarn twist. For example, even though the timing of the cams or solenoids or other control devices may be reasonably accurate and in phase with the yarn supply and node plying devices the timing of the air pulses at the twisting jet devices may be non-uniform. Such non-uniformity and lack of precision control makes it difficult to exactly control the spacing between the nodes. Exact uniformity of node length may be quite important, since the plying device, for example, a rotating knob, must hit the strands exactly at the nodes. If the length of the air lines differs, then the twisting jet devices closest to the air switches or other air control devices will respond relatively sooner and those further away will respond later.
It is difficult, if not impossible, to take account of that difference in timing by means of the control mechanism, for example, by repositioning the cams, since the degree of lateness depends on many factors, such as tubing diameter, tubing length, and changes of air pressure. Under some circumstances, where the tubing is particularly long, it may occur that, due to the length of transportation time between the control device and the vortex twist jet device, two or more opposite air pulse signals may occur within the interconnecting tubing at the same time. In the case of a duo-directional vortex jet, both the "S" and "Z" modes may operate simultaneously and no useable yarn twist would result since the air pulses would be in opposite directions.